Elrond is old even amongst the immortal Elves, having fought against Sauron in an earlier age and seen the Ring taken by Isildur before it was lost. He is the master of Rivendell and as such he has the power to command whole armies of Elven warriors. He is a highly competent warrior and a skilled spell caster, both of which make him a formidable adversary.
Gil-Galad was the mightiest warrior of his age and the leader of the Elves in the Last Alliance of Men and Elves against Sauron. He fell in that battle, but thanks to his sacrifice Sauron was defeated though not, alas, destroyed.